U.S. patent number 7,863,515 [Application Number 12/035,927] was granted by the patent office on 2011-01-04 for thin-film solar cell and method of manufacturing the same.
This patent grant is currently assigned to LG Electronics Inc.. Invention is credited to Seh-Won Ahn, Young-Joo Eo, Don-Hee Lee, Heon-Min Lee, Kwy-Ro Lee.
United States Patent |
7,863,515 |
Ahn , et al. |
January 4, 2011 |
Thin-film solar cell and method of manufacturing the same
Abstract
A thin-film solar cell having a first solar cell layer with a
plurality of unit cells including a photoelectric conversion layer
that are connected in series; a second solar cell layer with a
plurality of unit cells including a photoelectric conversion layer
that are connected in series, and that has band gap energy
different from the first solar cell layer and a threshold voltage
coincident with the first solar cell layer; and an electrode
connector, that connects the first solar cell layer with the second
solar cell layer in parallel.
Inventors: |
Ahn; Seh-Won (Seoul,
KR), Eo; Young-Joo (Seoul, KR), Lee;
Kwy-Ro (Seoul, KR), Lee; Don-Hee (Seoul,
KR), Lee; Heon-Min (Seoul, KR) |
Assignee: |
LG Electronics Inc. (Seoul,
KR)
|
Family
ID: |
39537922 |
Appl.
No.: |
12/035,927 |
Filed: |
February 22, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080264478 A1 |
Oct 30, 2008 |
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Foreign Application Priority Data
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Feb 26, 2007 [KR] |
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10-2007-0019097 |
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Current U.S.
Class: |
136/244; 438/67;
136/251; 438/66; 438/80; 438/74 |
Current CPC
Class: |
H01L
31/03923 (20130101); H01L 31/0392 (20130101); H01L
31/043 (20141201); H01L 31/076 (20130101); H01L
31/03925 (20130101); H01L 31/046 (20141201); H01L
31/02021 (20130101); Y02E 10/548 (20130101); H01L
2924/0002 (20130101); Y02P 70/50 (20151101); Y02E
10/541 (20130101); H01L 2924/0002 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
H01L
31/042 (20060101); H01L 21/02 (20060101); H01L
21/98 (20060101); H01L 31/05 (20060101) |
Field of
Search: |
;136/243-265
;438/57-98 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ridley; Basia
Assistant Examiner: Chern; Christina
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch, LLP
Claims
What is claimed is:
1. A thin-film solar cell, comprising: a substrate; a first solar
cell layer comprising a plurality of unit cells connected in series
on the substrate, wherein each unit cell includes a photoelectric
conversion layer; a second solar cell layer comprising a plurality
of unit cells connected in series on the first solar cell layer,
wherein each unit cell includes a photoelectric conversion layer;
and an electrode connector, which electrically connects the first
solar cell layer with the second solar cell layer in parallel,
wherein a number of the plurality of unit cells of the first solar
cell layer is different than a number of the plurality of unit
cells of the second solar cell layer, and the number of the
plurality of unit cells of the first solar cell layer and the
number of the plurality of unit cells of the second solar cell
layer are determined so that a threshold voltage of the first solar
cell layer is matched with a threshold voltage of the second solar
cell layer.
2. The thin-film solar cell of claim 1, wherein the second solar
cell layer has a band gap energy, which is different from a band
gap energy of the first solar cell layer.
3. The thin-film solar cell of claim 1, wherein the photoelectric
conversion layers is any one selected from a group consisting of
amorphous silicon, microcrystalline silicon, monocrystalline
silicon, polycrystalline silicon, amorphous SiC, amorphous SiN,
amorphous SiGe, amorphous SiSn, gallium arsenide (GaAs), aluminum
gallium arsenide (AlGaAs), indium phosphorus (InP), gallium
phosphorus (GaP), copper indium gallium selenide (CIGS), cadmium
telluride (CdTe), cadmium sulfide, copper sulfide (Cu.sub.2S), zinc
telluride (ZnTe), Plumbum sulfide (PbS), copper indium diselenide
(CulnSe.sub.2, CIS), gallium antimonide (GaSb) and compounds
thereof.
4. The thin-film solar cell of claim 1, wherein the first solar
cell layer and the second solar cell layer are any one selected
from an amorphous silicon solar cell layer and a microcrystalline
silicon solar cell layer.
5. The thin-film solar cell of claim 4, wherein the amorphous
silicon solar cell layer is formed such that a p-i-n type amorphous
silicon layer is consecutively stacked or a p-n type amorphous
silicon layer is consecutively stacked.
6. The thin-film solar cell of claim 4, wherein the
microcrystalline silicon solar cell layer is formed such that a
p-i-n type microcrystalline silicon layer is consecutively stacked
or a p-n type microcrystalline silicon layer is consecutively
stacked.
7. The thin-film solar cell of claim 1, further comprising a
transparent conductive layer provided at an upper part and a lower
part of the unit cells, respectively.
8. The thin-film solar cell of claim 7, wherein the unit cells are
connected in series by connecting an upper transparent conductive
layer of the unit cells with a lower transparent conductive layer
of adjacent unit cells.
9. The thin-film solar cell of claim 7, further comprising at least
one or more electrode connector configured of: a lower electrode
connector, which connects the lower transparent conductive layer of
each unit cell of the first solar cell layer with the lower
transparent conductive layer of each unit cell of the second solar
cell layer; and an upper electrode connector, which connects the
upper transparent conductive layer of each unit cell of the first
solar cell layer with the upper transparent conductive layer of
each unit cell of the second solar cell layer.
10. The thin-film solar cell of claim 9, wherein the first solar
cell layer and the second solar cell layer, which are connected by
the upper and lower electrode connectors, have the same width as
each other.
11. The thin-film solar cell of claim 9, wherein the upper
electrode connector and the lower electrode connector are formed at
the opposite side of cells, respectively.
12. The thin-film solar cell of claim 1, further comprising an
insulating layer formed between the first solar cell layer and the
second solar cell layer.
13. A method of manufacturing a thin-film solar cell, the method
comprising: forming a first solar cell layer by forming a plurality
of unit cells and connecting them in series on a substrate, wherein
each unit cell includes a photoelectric conversion layer; and
forming a second solar cell layer by forming a plurality of unit
cells and connecting them in series on the first solar cell layer,
wherein each unit cell includes a photoelectric conversion layer;
and electrically connecting the first solar cell layer with the
second solar cell layer in parallel, wherein a number of the
plurality of unit cells of the first solar cell layer is different
than a number of the plurality of unit cells of the second solar
cell layer, and the number of the plurality of unit cells of the
first solar cell layer and the number of the plurality of unit
cells of the second solar cell layer are determined so that a
threshold voltage of the first solar cell layer is matched with a
threshold voltage of the second solar cell layer.
14. The method of manufacturing the thin-film solar cell of claim
13, wherein the second solar cell layer has a band gap energy,
which is different from a band gap energy of the first solar cell
layer.
15. The method of manufacturing the thin-film solar cell of claim
13, further comprising the step of forming transparent conductive
layers at the upper part and lower part of the unit cells,
respectively.
16. The method of manufacturing the thin-film solar cell of claim
15, wherein the unit cells are connected in series by connecting an
upper transparent conductive layer of unit cells with a lower
transparent conductive layer of adjacent unit cells.
17. The method of manufacturing the thin-film solar cell of claim
15, further comprising at least one or more electrode connector
configured of: a lower electrode connector, which connects the
lower transparent conductive layer of each unit cell of the first
solar cell layer and the lower transparent conductive layer of each
unit cell of the second solar cell layer; and an upper electrode
connector, which connects the upper transparent conductive layer of
each unit cell of the first solar cell layer and the upper
transparent conductive layer of each unit cell of the second solar
cell layer.
18. The method of manufacturing the thin-film solar cell of claim
17, wherein the first solar cell layer and the second solar cell
layer, which are connected by the upper and lower electrode
connector, have the same width as each other.
19. The method of manufacturing the thin-film solar cell of claim
17, wherein the upper electrode connector and the lower electrode
connector are formed at the opposite side of the cells,
respectively.
20. The method of manufacturing the thin-film solar cell of claim
13, wherein the unit cells is patterned by any one method selected
from a laser scribing method, an optical scribing method, a
mechanical scribing method, an etching method using plasma, a
wet-type etching method, a dry-type etching method, a lift-off
method and a wire mask method.
21. The method of manufacturing the thin-film solar cell of claim
13, further comprising the step of forming an insulating layer
between the first solar cell layer and the second solar cell
layer.
22. The method of manufacturing the thin-film solar cell of claim
13, wherein the first solar cell layer and the second solar cell
layer is vertically stacked with an insulating layer
therebetween.
23. The method of manufacturing the thin-film solar cell of claim
13, wherein the first solar cell layer is formed by consecutively
stacking a p-i-n type amorphous silicon layer or a p-n type
amorphous silicon layer, and the second solar cell layer is formed
by consecutively stacking a p-i-n type microcrystalline silicon
layer or a p-n type microcrystalline silicon layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Patent Application
No. 10-2007-019097, filed on Feb. 26, 2007, in the Korean
Intellectual Property Office, the disclosure of which is
incorporated herein by reference.
BACKGROUND
1. Field of the Invention
The present invention relates to an integrated thin-film solar cell
module and a method of manufacturing the same, and more
particularly, to a thin-film solar cell and a method of
manufacturing the same, which are capable of improving a
photoelectric conversion efficiency.
2. Discussion of the Related Art
The research in solar cells as next generation clean energy
resources has been carried out for many years. Until recently, as
materials for solar cells, materials of group IV such as
monocrystalline silicon, polycrystalline silicon, amorphous
silicon, amorphous SiC, amorphous SiN, amorphous SiCe and amorphous
SiSn, and compound semiconductors of group III-V such as gallium
arsenide (GaAs), aluminum gallium arsenide (AlGaAs) and indium
phosphorus (InP) or group II-VI such as CdS, CdTe and Cu.sub.2S
have been used. Further, structures for the solar cell include a pn
structure including back electrode layer; a pin structure; a
heterojunction structure; a schottky structure; and a multiple
junction structure including tandem or vertical junction type.
In general, as the characteristics required for the solar cell,
there are a high photoelectric conversion efficiency, low
production costs and a short energy recovery period.
A solar cell using monocrystalline bulk silicon, which is being
commonly used at present, has a high photoelectric conversion
efficiency, but the fact is that it is not being actively utilized
due to high production and installation costs thereof. Research
into thin-film solar cells has been actively carried out to solve
such problems. Particularly, a thin-film solar cell using amorphous
silicon (a-Si:H), which is capable of reducing production costs of
large size solar cell modules and energy recovery period, has drawn
more attention. However, the thin-film solar cell has problems such
that the photoelectric conversion efficiency thereof is lower than
that of a monocrystalline silicon solar cell and the efficiency is
decreased when exposed to light.
For a solar cell using the other materials, in a case where the
photoelectric conversion efficiency thereof is high, fabrication
costs are increased and energy recovery period is extended, and in
contrast, low fabrication costs and a short energy recovery period
result in a low photoelectric conversion efficiency.
A structure including semiconductor layers having the different
band gap energy and a buffer layer formed therebetween has been
suggested to improve the above problems such as the low
photoelectric conversion efficiency of the thin-film solar cell
using amorphous silicon. Particularly, an up-down stack structure
of amorphous silicon (a-Si:H) and microcrystalline silicon
(uc-Si:H), which have the different band gap energy and crystal
lattice mismatch, has been suggested.
FIG. 1 is a sectional view illustrating a stack structure of a
thin-film solar cell module according to an example of the prior
art.
In the thin-film solar cell module according to the example of the
prior art shown in FIG. 1, a first solar cell layer 120 and a
second solar cell layer 130 with the different characteristics and
crystal structure consist of a stack structure and are electrically
connected in series by connecting a transparent conductive layer
111 stacked on the unit cell of the second solar cell 130 with a
transparent conductive layer 110 stacked under the adjacent unit
cell of the first solar cell layer 120.
FIG. 2 is an equivalent circuit diagram of a diode illustrating a
series connection of the semiconductor layers.
In general, a first solar cell layer toward incident sunlight
consists of amorphous silicon and has a high band gap energy of
about 1.7 to 1.9 eV, whereas, a second solar cell layer stacked
onto the first solar cell layer consists of microcrystalline
silicon and has a band gap energy of about 1.1 eV. Thus, since the
solar cell layers having different absorption bands are stacked,
the thin-film solar cell formed of both solar cell layers has a
higher photoelectric conversion efficiency as compared with the
thin-film solar cell formed of single solar cell layers. As a
result of the research, a small module having an area of 3 cm.sup.2
produces an initial photoelectric conversion efficiency of about
14.5% and a large area module produces an initial conversion
efficiency of about 12%.
However, the solar cell structure on which the different double
solar cell layers are stacked causes a problem such that the
current of both the solar cell layers should be designed to be
equal because both the solar cell layers are connected in series.
By such a restriction, the thickness of an amorphous silicon
intrinsic semiconductor layer of the first solar cell layer, which
is located at the lower part, should be thickly formed beyond what
is otherwise needed, and in proportion to the thickness, as the
electric power rate generated at the amorphous solar cell layer
become high, the total efficiency due to the Stabler-Wronski effect
is excessively decreased. Conversely, in the case that the
thickness of the intrinsic semiconductor layer is most suitable and
thin, a short-circuit current of the first solar cell layer located
at a lower part become small, and thus, as the difference of the
short-circuit current between both the solar cell layers is
increased, the total efficiency of the element in which two layers
are connected in series is reduced compared with the total
efficiency achieved by both solar cell layers because the whole
short-circuit current is limited by the short-circuit current of
the first solar cell layer.
In order to get over a difficulty of manufacturing process such
that it is not easy to adjust the thickness of intrinsic
semiconductor for producing an optimal photoelectric conversion
efficiency at solar cells on which the different double solar cell
layers are stacked, and in order to establish a stable reliability
in a regular efficiency of manufactured solar cells, U.S.
publication patent No. 2005/0150542 A1 discloses a solar cell
module such that a first solar cell layer 220 and a second solar
cell layer 230 are respectively connected to an adjacent cell in
series, by separating the first solar cell layer 220 located toward
the lower part from the second solar cell layer 230 located toward
the upper part by a transparent insulating layer and providing a
4-T structure which draws two terminals from each solar cell
layer.
FIG. 3 is a sectional view illustrating a stack structure of a
4-terminal thin-film solar cell module, which is disclosed in the
above U.S. patent, and FIG. 4 is a diode equivalent circuit of the
4-terminal thin-film solar cell module.
SUMMARY OF THE INVENTION
The present invention has been suggested to solve the problems. It
is an object of the present invention to provide a thin-film solar
cell having a structure, which is capable of improving a
photoelectric conversion efficiency and a method of manufacturing a
thin-film solar cell, which is capable of reducing fabrication
costs compared with the other thin-film silicon solar cells by
manufacturing the solar cell through a relatively simple
process.
It is another object of the present invention to provide a
thin-film solar cell structure and a method of manufacturing the
same, which are capable of minimizing the power loss by a mismatch
in short-circuit currents, with respect to a solar cell having a
structure in which two solar cell layers having great differences
between short-circuit currents thereof and different
characteristics are stacked.
It is yet another object of the present invention to provide a
method of simply manufacturing a thin-film solar cell through a
series of manufacturing processes, which is capable of improving a
photoelectric conversion efficiency and solving complicated
manufacturing processes of the prior art, with respect to a solar
cell having a structure in which two solar cell layers having great
differences between short-circuit currents thereof and different
characteristics are stacked, in a way such that a first solar cell
layer and a second solar cell layer are separately manufactured and
connected.
In accordance with an aspect of the present invention, the above
and other objects can be accomplished by the provision of a
thin-film solar cell comprising: a first solar cell layer, in which
a plurality of unit cells including photoelectric conversion layers
are connected in series; a second solar cell layer, in which a
plurality of unit cells including the photoelectric conversion
layers are connected in series; and an electrode connector, which
connects the first solar cell layer with the second solar cell
layer.
In the present invention, the second solar cell layer has a band
gap energy, which is different from the first solar cell layer, and
a threshold voltage, which is coincident with the first solar cell
layer.
The photoelectric conversion layers according to the present
invention should not be construed as being limited to the above
example embodiments and it will be apparent to those skilled in the
art that modifications and variations can be made to the example
embodiments of the present invention without deviating therefrom.
Preferably, the photoelectric conversion layers is any one selected
from a group consisting of amorphous silicon, microcrystalline
silicon, monocrystalline silicon, polycrystalline silicon,
amorphous Sic, amorphous SiN, amorphous SiGe, amorphous SiSn,
gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium
phosphorus (InP), gallium phosphorus (GaP), copper indium gallium
selenide (CIGS), cadmium telluride (CdTe), cadmium sulfide, copper
sulfide (Cu.sub.2S), zinc telluride (ZnTe), Plumbum sulfide (PbS),
copper indium diselenide (CulnSe.sub.2, CIS), gallium antimonide
(GaSb) and compounds thereof.
In the present invention, the first solar cell layer and the second
solar cell layer may be any one selected from an amorphous silicon
solar cell layer and a microcrystalline silicon solar cell layer.
Preferably, the amorphous silicon solar cell layer may be formed
such that a p-i-n type amorphous silicon layer is consecutively
stacked or a p-n type amorphous silicon layer is consecutively
stacked.
Further, the microcrystalline silicon solar cell layer may be
formed such that a p-i-n type microcrystalline silicon layer is
consecutively stacked or a p-n type microcrystalline silicon layer
is consecutively stacked.
A series connection of the unit cells according to the present
invention may be provided with each transparent conductive layer at
an upper part and a lower part of the unit cells and is
characterized by connecting an upper transparent conductive layer
of the unit cells with a lower transparent conductive layer of
adjacent unit cells.
A thin-film solar cell comprises at least one or more electrode
connector.
Preferably, a electrode connector consists of a lower electrode
connector, which connects the lower transparent conductive layer of
each unit cell of the first solar cell layer with the lower
transparent conductive layer of each unit cell of the second solar
cell layer, and an upper electrode connector, which connects the
upper transparent conductive layer of each unit cell of the first
solar cell layer with the upper transparent conductive layer of
each unit cell of the second solar cell layer.
The first solar cell layer and the second solar cell layer are
provided with each transparent conductive layer at the upper part
and lower part of the unit cells thereof, and are connected in
series by connecting the upper transparent conductive layer of each
unit cell with the lower transparent conductive layer of an
adjacent unit cell.
Preferably, the first solar cell layer and the second solar cell
layer connected by the upper and lower electrode connectors have
the same width as each other.
In other words, the number of unit cells of the first solar cell
layer and the second solar cell layer which are included between at
least a couple of the upper electrode connector and lower electrode
connector, can be adjusted so that the first solar cell layer and
the second solar cell layer have the same width as each other.
When the thin-film solar cell of the present invention is
manufactured, each number of the unit cells is previously
calculated so that a threshold voltage of the first solar cell
layer and the second solar cell layer is the same as each other,
thereby determining the patterning of the unit cells of the solar
cell.
In the present invention, stack shapes or arrangements of the first
solar cell layer and the second solar cell layer should be not
construed as being limited to example embodiments set forth herein,
as well as they could be easily achieved by those skilled in the
art, and preferably, the first solar cell layer and the second
solar cell layer may be vertically stacked with an insulating layer
therebetween.
To achieve the above-mentioned objects, a method of manufacturing a
thin-film solar cell of the present invention comprises the steps
of: forming a first solar cell layer by forming a plurality of unit
cells including a photoelectric conversion layer and connecting
them in series; forming a second solar cell layer by forming a
plurality of unit cells including a photoelectric conversion layer
and connecting them in series; and electrically connecting the
first solar cell layer with the second solar cell layer in
parallel.
In the present invention, the second solar cell layer may have a
band gap energy, which is different from the first solar cell
layer, and a threshold voltage, which is coincident with the first
solar cell layer.
Preferably, the thin-film solar cell of the present invention
further comprises the step of forming transparent conductive layers
at the upper part and lower part of the unit cells,
respectively.
Further, the unit cells may be patterned by any one selected from a
laser scribing method, an optical scribing method, a mechanical
scribing method, an etching method using plasma, a wet-type etching
method, a dry-type etching method, a lift-off method and a wire
mask method.
Preferably, the method of manufacturing the thin-film solar cell of
the present invention further comprises the step of forming an
insulating layer between the first solar cell layer and the second
solar cell layer.
A series connection of the unit cells according to the present
invention may be provided with each transparent conductive layer at
an upper part and a lower part of the unit cells and is
characterized by connecting an upper transparent conductive layer
of the unit cells with a lower transparent conductive layer of
adjacent unit cells.
Preferably, an electrode connector is provided with each
transparent conductive layer at the upper part lower part of the
unit cells of the first solar cell layer and the second solar cell
layer, which are formed by connecting the upper transparent
conductive layer of unit cells with the lower transparent
conductive layer of an adjacent unit cell in series comprising at
least one or more electrode connector, which consists of a lower
electrode connector, which connects the lower transparent
conductive layer of each unit cell of the first solar cell layer
with the lower transparent conductive layer of each unit cell of
the second solar cell layer; and an upper electrode connector,
which connects the upper transparent conductive layer of each unit
cell of the first solar cell layer with the upper transparent
conductive layer of each unit cell of the second solar cell
layer.
Preferably, the first solar cell layer and the second solar cell
layer, which are connected by the upper and lower electrode
connector, have the same width as each other.
The first solar cell layer and the second solar cell layer
according to manufacturing methods of the present invention may be
vertically stacked with an insulating layer therebetween, but it
should not be construed as being limited to this embodiment and may
be embodied in many different forms.
Further, the first solar cell layer may be formed by consecutively
stacking a p-i-n type amorphous silicon layer or a p-n type
amorphous silicon layer and the second solar cell layer may be
formed by consecutively stacking a p-i-n type microcrystalline
silicon layer or a p-n type microcrystalline silicon layer
A method of manufacturing a thin-film solar cell according to the
present invention comprises the steps of: stacking and patterning a
lower transparent conductive layer of a first solar cell layer on a
substrate; stacking and patterning an amorphous silicon p-i-n layer
or amorphous silicon p-n layer on a lower transparent conductive
layer of the first solar cell layer; forming an upper transparent
conductive layer of the first solar cell layer on the amorphous
silicon layer and connecting it with the lower transparent
conductive layer; forming at least one or more unit cell of the
first solar cell layer by patterning the upper transparent
conductive layer; forming an insulating layer on unit cells of the
first solar cell layer; stacking and patterning the lower
transparent conductive layer of a second solar cell layer on the
insulating layer; connecting the lower transparent conductive layer
of the first solar cell layer with the lower transparent conductive
layer of the second solar cell layer through a lower electrode
connector; stacking and patterning a microcrystalline silicon p-i-n
layer or a microcrystalline silicon p-n layer on the lower
transparent conductive layer of the second solar cell layer;
forming at least one or more unit cell of the second solar cell
layer by further forming the upper transparent conductive layer of
the second solar cell layer on the microcrystalline silicon layer
and connecting it with the lower transparent conductive layer of
the second solar cell layer; and further forming a back-side
electrode layer on the upper transparent conductive layer of the
second solar cell layer and connecting the back-side electrode
layer or the upper transparent conductive layer of the second solar
cell layer with the upper transparent conductive layer of the first
solar cell layer by the upper electrode connector.
The lower electrode connector and upper electrode connector are
formed at a distance so that the first solar cell layer and the
second solar cell layer have the same width as each other.
The lower electrode connector and the upper electrode connector
form a pair of electrode connectors and at least one or more
electrode connector may be formed at a large area thin-film solar
cell.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects, features, and advantages of preferred
embodiments of the present invention will be more fully described
in the following detailed description, taken in conjunction with
the accompanying drawings. In the drawings:
FIG. 1 is a sectional view illustrating a stack structure of a
thinfilm solar cell module according to an example of the prior
art.
FIG. 2 is a diode equivalent circuit diagram of the thin film solar
cell module according to the example of the prior art.
FIG. 3 is a sectional view illustrating a stack structure of a
4-terminal thin-film solar cell module according to another example
of the prior art.
FIG. 4 is a diode equivalent circuit of a 4-terminal thin-film
solar cell module according to the example of the prior art.
FIG. 5 is a sectional view illustrating a stack structure of the
thin-film solar cell module according to a preferred embodiment of
the present invention.
FIG. 6 is a diode equivalent circuit of the thin-film solar cell
module according to the preferred embodiment of the present
invention.
FIG. 7 is a graph illustrating the relationship between
short-circuit current density-voltage for the thin-film solar cell
module according to the preferred embodiment of the present
invention and the thin-film solar cell module according to an
example embodiment of the prior art.
FIG. 8 is a graph illustrating the relationship between the
efficiency-voltage for the thin-film solar cell module according to
the preferred embodiment of the present invention and the thin-film
solar cell module according to an example embodiment of the prior
art.
FIG. 9 to FIG. 24 are sectional views illustrating a stack
structure of modules representing a method of manufacturing the
thin-film solar cell in response to process steps according to the
preferred embodiment of the present invention.
FIG. 25 is a top plan view illustrating the thin-film solar cell
module according to the preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Embodiments of the present invention will now be described
hereafter with reference to the attached drawings. Reference
numerals added to construction elements of each drawings use the
same numerals within the range of the same construction elements,
even though they are indicated in the other drawings, and the
detailed description about well-known functions and structures,
which are outside the subject matter of the present invention will
be omitted.
FIG. 5 is a sectional view illustrating a stack structure of the
thin-film solar cell module according to the preferred embodiment
of the present invention and FIG. 6 is a diode equivalent circuit
of the thin-film solar cell module according to the preferred
embodiment of the present invention.
In the preferred embodiment of the present invention, the thin-film
solar cell is formed by stacking a substrate 300, the first solar
cell layer 320, the second solar cell layer 330 and the back-side
electrode layer 340; transparent conductive layers 310 and 311 are
provided at the lower part and upper part of the first solar cell
layer 320, respectively and transparent conductive layers 312 and
313 are provided at the lower part and upper part of the second
solar cell layer 330, respectively; and the first solar cell layer
320 and the second solar cell layer 330 are electrically separated
from each other by an insulating layer 350 therebetween. Further,
the example embodiment has a structure that the first solar cell
layer 320 and the second solar cell layer 330 may be stacked up and
down and provided with the insulating layer therebetween, but is
not limited to this structure, thereby there is not any limitation
for arrangement shapes of both the solar cell layers.
Electrically connecting the first solar cell layer 320 with the
second solar cell layer 330 in parallel may be carried out by an
electrode connector 360a for connecting the lower transparent
conductive layer 310 of first solar cell layer 320 and the lower
transparent conductive layer 312 of the second solar cell layer 330
and an electrode connector 360b for connecting the upper
transparent conductive layer 311 of first solar cell layer 320 and
the upper transparent conductive layer 313 of the second solar cell
layer 330.
The upper electrode connector 360b of both the solar cell layers
may be connected to a backside electrode layer 340 which is
provided at the upper part of the second solar cell layer 330.
Referring to FIG. 5, the thin-film solar cell layer according to
the preferred embodiment of the present invention consists of a
multiple junction structure of a plurality of unit cells separated
by patterning and these unit cells are electrically connected in
series by the transparent conductive layer formed at the upper part
and the lower part of each solar cell layer. A plurality of the
unit cells are electrically connected in series, thereby forming an
integrated large area thin-film solar cell.
The series connection between the unit cells is achieved through an
insulating layer 350 formed between adjacent unit cells.
In the above example embodiment, the thin-film solar cell has gaps
formed between unit cells by patterning from the top and isolation
processes, consecutively, to a back-side electrode layer 340, the
upper transparent conductive layer 313 and p layer 331 of the
second solar cell layer 330, and an air in the gaps can be
performed as an insulating layer and adjacent unit cells are
electrically connected in series.
Two solar cell layers consisting of the unit cells, which are
connected in series, namely, the first solar cell layer 320 and the
second solar cell layer 330 are connected in parallel by the
electrode connectors 360a, 360b.
Semiconductor materials that form the first solar cell layer 320
and the second solar cell layer 330 may be formed of materials,
which are different from each other having different
characteristics. Namely, they may consist of semiconductor
materials having different band gap energy.
The thin-film solar cell according to the preferred embodiment of
the present invention may be formed of amorphous silicon and
microcrystalline silicon. Particularly, the first solar cell layer
320 stacked on a glass substrate 300 may be made of amorphous
silicon and the second solar cell layer 330 also may be made of
microcrystalline silicon. In case of this embodiment, a band gap
energy of the amorphous silicon semiconductor layer is 1.7 eV to
1.9 eV and a band gap energy of the microcrystalline silicon
semiconductor layer is 1.1 eV.
However, these examples are provided only for illustrating the
present invention and should not be construed as limiting the scope
of the present invention. Thus, any one among general semiconductor
materials such as amorphous silicon, microcrystalline silicon,
monocrystalline silicon, polycrystalline silicon, amorphous SiC,
amorphous SiN, amorphous Sie, amorphous SiSn, gallium arsenide
(GaAs), aluminum gallium arsenide (AlGaAs), indium phosphorus
(InP), gallium phosphorus (GaP), copper indium gallium selenide
(CIGS), cadmium telluride (CdTe), cadmium sulfide, copper sulfide
(Cu.sub.2S), zinc telluride (ZnTe), Plumbum sulfide (PbS), copper
indium diselenide (CulnSe.sub.2; CIS), gallium antimonide (GaSb)
and compounds thereof may be selected.
One solar cell layer may be formed by stacking a semiconductor
layer having p-i-n or p-n type junction structure.
Preferably, the first solar cell layer 320 stacked on a glass
substrate 300 may be formed by stacking a p-type semiconductor
layer 321, an i-type semiconductor layer 322, and a n-type
semiconductor layer 323.
Also, the second solar cell layer 330 may be formed by stacking a
p-type semiconductor layer 331, an i-type semiconductor layer 332,
and a n type semiconductor layer 333.
A threshold voltage of unit cell that forms both the solar cell
layers is different from each other because the semiconductor
materials that form the first solar cell layer and the second solar
cell layer are formed of the materials, which are different from
each other having the different band gap characteristics.
In the present invention, when the length that both the solar cell
layers are connected in parallel by the electrode connector become
one solar cell unit module, it should be configured so that
threshold voltages of each solar cell layer within the unit module
are nearly coincident with each other. Since the difference between
the short-circuit currents is increased and the total efficiency of
the solar cell module is reduced by the different band gap energy
of semiconductor materials that form each solar cell layer, it is
necessary that the threshold voltages of each solar cell layer
within the unit module are nearly coincident with each other.
For this, the number of unit cell that forms each solar cell layer
is adjusted and patterned accordingly.
As one embodiment, in a case where a threshold voltage of
semiconductor material of the first solar cell layer is 0.70V and
that of the second solar cell layer is 0.47V, the number of unit
cells of the first solar cell layer provided within a unit module,
which is connected in parallel by a pair of electrode connectors,
is 2 unit cells and the number of unit cells of the second solar
cell layer becomes 3 unit cells.
In this case, at one unit module, since the total threshold voltage
that forms two unit cells of the first solar cell layer is 1.40V
and the total threshold voltage that forms the three unit cells of
the second solar cell layer is 1.41V, the threshold voltages of
both the solar cell layers are nearly coincident with each other.
Thus, the photoelectric conversion efficiency is not reduced by the
difference of the threshold voltage, thereby obtaining the solar
cell module having a high efficiency.
In the above example embodiment, it is preferable that the first
solar cell layer and the second solar cell layer within the unit
module formed by a couple of electrode connectors have the same
width as each other, and thus, the width of the unit cells of the
first solar cell layer and the second solar cell layer become
different from each other so that the number of the unit cells of
the first solar cell layer and the second solar cell layer are
provided to be within the same width for obtaining the threshold
voltages, which are nearly coincident with each other, and thus
patterned accordingly.
Referring to FIG. 5, since the number of unit cells of the first
solar cell layer provided at the width between the identical unit
module is 2 unit cells and the number of the unit cells of the
second solar cell layer is 3 unit cells, the width of unit cells of
the first solar cell layer is greater than that of the second solar
cell layer.
Referring to FIG. 6, which is an equivalent circuit diagram of the
solar cell according to the above embodiment, the first solar cell
layer and the second solar cell layer have the unit cells of the
different numbers so that the threshold voltages are respectively
matched with each other, and are connected in parallel, thereby
obtaining 2 terminals as a general solar cell, which is different
from obtaining 4 terminals as a result that the conventional 4-T
type thin-film solar cell as shown in FIGS. 3 and 4 has insulating
layers between both the solar cell layers stacked at the upper part
and lower part so as to be electrically separated.
Accordingly, output voltages of the solar cell layers of the upper
and lower parts may be efficiently combined and, obtaining 2
terminals can lead to high economic effectiveness in respect to the
fabrication processes or costs.
The number of unit cells of each layers is calculated so that the
threshold voltages of the first solar cell layer and the second
solar cell layer formed of semiconductor materials having different
characteristics are matched, and the width of the unit cell for the
number of unit cells included within the unit module having a
predetermined width is calculated, thereby achieving an integrated
large area thin-film solar cell.
The process of inducing a photovoltaic effect from the element of
the thin-film solar cell is started while light incident through
the glass substrate penetrates a p type silicon layer of the first
solar cell layer or the second solar cell layer and is then
absorbed into an i type silicon layer.
In a case where the energy of the above incident light is larger
than that of an optical band gap of amorphous silicon or
microcrystalline silicon, an electron is excited and an
electron-hole pair is generated. The generated electron and hole
are separated into n type silicon layer and p type silicon layer,
by an internal field, respectively, and moved, thus, when a
photovoltaic power generated between the pole tip of the p type and
n type layers is connected to the outside circuit, the solar cell
is operated.
Referring to the equivalent circuit diagram of FIG. 6, a
photovoltaic power is induced at the first solar cell layer 320
located at the lower part and the second solar cell layer 330
located at the upper part. A unit module connected in parallel is
formed by connecting the solar cell layers 320 and 330 by electrode
connectors 360a, 360b and is connected to the outside circuit to
operate the solar cell.
The above embodiment can lead to effects such as simple manufacture
methods and reduced fabrication costs because the number of unit
cells is adjusted so that the threshold voltage is matched while a
stack structure of the solar cell layers having two different
characteristics is kept, and a structure between layers is adjusted
through patterning using stack orders and isolation process within
a range of manufacture methods of the conventional solar cell so
that each solar cell layer is electrically connected in parallel.
Hereinafter, the detailed manufacture method will be described.
FIG. 7 is a graph illustrating the relationship between
short-circuit current density-voltage for thin-film solar cell
modules according to the preferred embodiment of the present
invention and the thin-film solar cell module according to the
preferred embodiment of the prior art and FIG. 8 is a graph
illustrating the relationship between efficiency-voltage for the
thin-film solar cell modules according to the preferred embodiment
of the present invention and the thin-film solar cell module
according to the preferred embodiment of the prior art.
The structure of the thin-film solar cell modules according to the
prior art in FIG. 7 and FIG. 8 has the same structure as shown in
FIG. 1. The solar cell according to the prior art shown in FIG. 3
is excluded from comparison objects because it has a structure that
the voltages of the solar cell layer of the upper part and lower
part are not combined together.
Referring to FIG. 1, the lower solar cell layer generally consists
of an amorphous silicon (a-Si:H) solar cell layer and it is
supposed that a stand-off voltage (Voc) is 0.90 V and the
short-circuit current density (Jsc) is 8.0 mA/cm.sup.2, and at that
time, the efficiency is about 5.4%. Further, the upper solar cell
layer generally consists of a microcrystalline silicon (uc-Si:H)
solar cell layer, and it is supposed that Voc is 0.62V, Jsc is 20
mA/cm.sup.2 and the efficiency is 9.3%
In a case where both the solar cell layers are connected in series
by the conventional method as shown in FIG. 1, Voc is 1.52 V, Jsc
is 8 mA/cm.sup.2 and the efficiency is about 10.0%, these are
indicated as a gray solid line in FIGS. 7 and 8. It has a result
that the efficiency is not increased because of mismatching of the
short-circuit current.
However, according to the preferred embodiment of the present
invention, in a case where two unit cells of the first solar cell
layer are connected in series, Voc is 1.80 V, Jsc is 4 mA/cm.sup.2,
and in a case where three unit cells of the second solar cell layer
are connected in series, Voc is 1.86 V and Jsc is 6.7 mA/cm.sup.2,
and thus, the threshold voltages become nearly coincident with each
other. Accordingly, in a case of parallel connection, Voc is 1.84 V
and Jsc is 10.7 mA/cm.sup.2, and the efficiency is 14.8% which
results in an increase in the efficiency of about 4.8% compared
with the efficiency of the conventional solar cell module. The
short-circuit current density and efficiency of the present
invention are indicated by a gray solid line in FIGS. 7 and 8.
FIG. 9 to FIG. 24 are sectional views of a stack structure of
modules illustrating a method of manufacturing the thin-film solar
cell in response to process steps according to the preferred
embodiment of the present invention.
A manufacture method according to the preferred embodiment of the
present invention comprises the steps of: forming a first solar
cell layer; forming a second solar cell layer formed of
semiconductor materials having band gap energy which are different
from the first solar cell layer; and electrically connecting the
first solar cell layer with the second solar cell layer in
parallel, and further comprises processes of providing a
transparent conductive layer at an upper part and a lower part of
each solar cell layer and forming a back-side electrode layer at
the upper part of the second solar cell layer.
To the structure wherein the first solar cell layer and the second
solar cell layer may be consecutively stacked up and down, a
process for forming insulating layers between both the solar cells
is added.
The detailed process according to the preferred embodiment of the
present invention may be divided into steps as follows:
(FIG. 9) The transparent conductive layer 310, which preferably
comprises a transparent conductive oxide(TCO), is firstly stacked
on a glass substrate 300.
The above substrate is not limited to the glass substrate.
(FIG. 10) The first transparent conductive layer 310 is patterned
using a laser scribing process.
The process of patterning is not limited to the laser scribing
method and methods, which could be easily conceived by those
skilled in the art based on the well-known art, may be used.
In general, as methods of patterning, a laser scribing method, an
optical scribing method, mechanical scribing method, etching method
using plasma, wet-type etching methods, dry type etching methods,
lift off method and wire mask method have been used.
(FIG. 11) A p-type amorphous silicon (a-Si:H) layer is stacked.
(FIG. 12) An i-type amorphous silicon (a-Si:H) layer is
stacked.
(FIG. 13) An n type amorphous silicon (a Si:H) layer is
stacked.
(FIG. 14) The unit cell is formed by using a laser scribing
process.
(FIG. 15) A transparent conductive layer 311 is secondly
stacked.
(FIG. 16) The first solar cell layer is patterned by using the
laser scribing process. At this time, it is patterned except for a
region, with which the first transparent conductive layer 310 and
the second transparent conductive layer 311 are connected.
(FIG. 17) An insulating layer 350 and a third transparent
conductive layer 312 are consecutively stacked.
(FIG. 18) The third transparent conductive layer is patterned using
the laser scribing process. The line width is different from the
width of the unit cell of the first solar cell layer as designed
for matching of the threshold voltage.
(FIG. 19) An electrode connector 360a, which connects the
transparent conductive layer 310 for the lower electrode of the
first solar cell layer with the transparent conductive layer 312
for the lower electrode of the second solar cell layer, is formed
at one part of unit cell. Materials of forming the electrode
connector may be conductive materials such as metal.
(FIG. 20) Microcrystalline silicon (un-Si:H) p layer 331, i layer
332 and n layer 333 are consecutively stacked.
(FIG. 21) The microcrystalline silicon layer is patterned so that
the unit cell of the second solar cell layer is formed using the
laser scribing process. At this time, pattering is performed
according to a pattern of the transparent conductive layer 312,
which is thirdly stacked.
(FIG. 22) A transparent conductive layer 313 is fourthly stacked
and a back-side metal electrode layer 340 is consecutively stacked
thereon.
(FIG. 23) The second solar cell layer is patterned using the laser
scribing process. At this time, it is patterned except a region
between the unit cells, from which the third transparent conductive
layer 312 and the fourth transparent conductive layer 313 are
connected so that the unit cells of the second solar cell layer are
connected in series.
(FIG. 24) An electrode connector 360b, which connects the
transparent conductive layer 311 for the upper electrode of the
first solar cell layer with the transparent conductive layer 313
for the upper electrode of the second solar cell layer, is formed
at one side of unit cell of the second solar cell layer opposite to
the electrode connector 360a. The electrode connector 360b may be
connected to the back side electrode layer 340 instead of the
transparent conductive layer 313 for the upper electrode of the
second solar cell layer.
A pair of electrode connectors 360a, 360b may be separately
connected as the above example embodiment, and simultaneously
connected after all process is finished.
FIG. 25 is a top plan view illustrating the thin-film solar cell
module according to the preferred embodiment of the present
invention.
In the step of the above fabrication method, as a method of forming
the electrode connectors of the first solar cell layer and the
second solar cell layer, as shown in FIG. 25, upper electrodes of
both the solar cell layers are connected with each other at one
side of the module and lower electrodes of both the solar cell
layers are connected with each other at the other side of the
module.
It is not necessary that the upper electrode connection site is
directly opposite to the lower electrode connection site and it is
possible to connect the upper and lower electrodes at any site
within the unit cells of the solar cell layer.
The present invention may be used for providing a solar cell having
a thin-film solar cell structure, which is capable of increasing a
photoelectric conversion efficiency and a stable reliability and
may be utilized for a method of manufacturing the solar cell, which
is capable of producing a large area solar cell through a
relatively simple process and at low fabrication costs.
Further, the present invention provides a structure of the solar
cell and a method of manufacturing the same, which are capable of
having a high photoelectric conversion efficiency and producing
solar cells having large area at low-costs, and accordingly, will
contribute to protecting earth's environment by providing clean
energy resources for the next generation and create great economic
benefit by its application to public facilities, private
facilities, munitions facilities and other various fields.
Although the present invention has been described in detail
reference to its presently preferred embodiment, it will be
understood by those skilled in the art that various modifications
and equivalents can be made without departing from the spirit and
scope of the present invention, as set forth in the appended
claims.
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